This investigation aims to explore the effects of stress conditions and rock cutting rates on hard rock fragmentation through indentation tests on a newly designed triaxial testing apparatus.This apparatus was designe...This investigation aims to explore the effects of stress conditions and rock cutting rates on hard rock fragmentation through indentation tests on a newly designed triaxial testing apparatus.This apparatus was designed to realize a triaxial loading and indentation test of cylindrical specimens using inserted tooth cutter.The boreability and crushing efficiency of granite rock was investigated by analyzing the change rules of the thrusting force,penetration depth,characteristics of chippings and failure patterns.Several quantitative indexes were used to evaluate rock boreability in this investigation.The granite rock samples all had a chiselled pit and a crushed rock core.Under initial stress conditions,only flat-shape chippings were stripped from the rock surface when the thrusting force reached 20 kN.The rock cutting special energy had a close correlation with the initial stress conditions and inserted tooth shape.Moreover,a thrusting force prediction model was proposed in this paper.The contribution of this study is that for the first time the influence mechanism of the initial triaxial stress conditions on rock fragmentation is investigated using an inserted tooth and the newly designed testing apparatus.This study has a crucial importance for practical underground hard rock crushing in geoengineering.展开更多
The oxidation tests of Ti_3AlC_2 were conducted at 1100 and 1200？C in air for 48 and 360 h, respectively,and the effects of high temperature oxidation on the flexural strength and hardness of Ti_3AlC_2 were investiga...The oxidation tests of Ti_3AlC_2 were conducted at 1100 and 1200？C in air for 48 and 360 h, respectively,and the effects of high temperature oxidation on the flexural strength and hardness of Ti_3AlC_2 were investigated. The microstructure, grain size and phase compositions of Ti_3AlC_2 substrate didn＇t change after oxidation, hence the oxide removed Ti_3AlC_2 substrate maintained its initial flexural strength and hardness. However, the flexural strength of oxide retained Ti_3AlC_2 decreased by about 5%. Acoustic emission monitoring indicated that during the process of three-point bending test, the formed Al_2O_3 scale on Ti_3AlC_2 surface fractured firstly in a cleavage manner, then the substrate/oxide interface cracked,and finally the Ti_3AlC_2 substrate fractured. The mechanical degradation was caused by the preferential formation of cracks in brittle Al_2O_3 scale as well as at defective and lacunose grain boundaries of the substrate where stress concentration generated. The mechanical degradation was insensitive to oxidation temperature and time in the present conditions. In addition, the surface hardness increased significantly after oxidation due to the formed hard Al_2O_3 scale on the surface of Ti_3AlC_2 substrate.展开更多
Rail surfaces are often damaged under constant loading,making repair of these areas essential for optimal performance in a railroad network.However,the traditional methods of improving rails are expensive and time-con...Rail surfaces are often damaged under constant loading,making repair of these areas essential for optimal performance in a railroad network.However,the traditional methods of improving rails are expensive and time-consuming,and require excessive effort.Therefore,some creative ideas would be helpful in this process,one of which may be on-site overlay arc welding instead of exchanging the whole part of the rail.In this paper,the performance of such a method is assessed experimentally,and its results are interpreted.For the investigation,a worn part of the 136RE rail,used in the freight railway network in the U.S.,was chosen.After milling and flattening the surface of the rail,a submerged arc welding(SAW)process was used to rebuild this rail by utilizing a 1/8-in Lincore 40-S depositing wire.This study used four destructive tests:1)XRD residual stress measurement,2)SEM/OM analysis,3)hardness test,and 4)tensile test.The results showed that the required mechanical strength could be achieved.However,the repaired area seems more vulnerable to the forces encountered on a railroad network due to the more brittle structure due to high temperatures in this region.Considering this flaw is critical because forces are primarily dynamic in railway networks,especially in heavy rails,which are higher due to the extensive use of freight trains.展开更多
基金The authors gratefully acknowledge the financial support from Natural Science Research Project of Universities in Anhui Province(No.KJ2021A0463)Scientific Research Startup Fund for introduced talents of Anhui University of Science and Technology,and Natural Science Foundation of Anhui Province(No.2108085QE208).
文摘This investigation aims to explore the effects of stress conditions and rock cutting rates on hard rock fragmentation through indentation tests on a newly designed triaxial testing apparatus.This apparatus was designed to realize a triaxial loading and indentation test of cylindrical specimens using inserted tooth cutter.The boreability and crushing efficiency of granite rock was investigated by analyzing the change rules of the thrusting force,penetration depth,characteristics of chippings and failure patterns.Several quantitative indexes were used to evaluate rock boreability in this investigation.The granite rock samples all had a chiselled pit and a crushed rock core.Under initial stress conditions,only flat-shape chippings were stripped from the rock surface when the thrusting force reached 20 kN.The rock cutting special energy had a close correlation with the initial stress conditions and inserted tooth shape.Moreover,a thrusting force prediction model was proposed in this paper.The contribution of this study is that for the first time the influence mechanism of the initial triaxial stress conditions on rock fragmentation is investigated using an inserted tooth and the newly designed testing apparatus.This study has a crucial importance for practical underground hard rock crushing in geoengineering.
基金financial support of the project from the National Natural Science Foundation of China (Nos. 51571205 and 51271191)
文摘The oxidation tests of Ti_3AlC_2 were conducted at 1100 and 1200？C in air for 48 and 360 h, respectively,and the effects of high temperature oxidation on the flexural strength and hardness of Ti_3AlC_2 were investigated. The microstructure, grain size and phase compositions of Ti_3AlC_2 substrate didn＇t change after oxidation, hence the oxide removed Ti_3AlC_2 substrate maintained its initial flexural strength and hardness. However, the flexural strength of oxide retained Ti_3AlC_2 decreased by about 5%. Acoustic emission monitoring indicated that during the process of three-point bending test, the formed Al_2O_3 scale on Ti_3AlC_2 surface fractured firstly in a cleavage manner, then the substrate/oxide interface cracked,and finally the Ti_3AlC_2 substrate fractured. The mechanical degradation was caused by the preferential formation of cracks in brittle Al_2O_3 scale as well as at defective and lacunose grain boundaries of the substrate where stress concentration generated. The mechanical degradation was insensitive to oxidation temperature and time in the present conditions. In addition, the surface hardness increased significantly after oxidation due to the formed hard Al_2O_3 scale on the surface of Ti_3AlC_2 substrate.
基金supported by the University Transportation Center(UTC)program of the U.S.Department of Transportation(DOT).
文摘Rail surfaces are often damaged under constant loading,making repair of these areas essential for optimal performance in a railroad network.However,the traditional methods of improving rails are expensive and time-consuming,and require excessive effort.Therefore,some creative ideas would be helpful in this process,one of which may be on-site overlay arc welding instead of exchanging the whole part of the rail.In this paper,the performance of such a method is assessed experimentally,and its results are interpreted.For the investigation,a worn part of the 136RE rail,used in the freight railway network in the U.S.,was chosen.After milling and flattening the surface of the rail,a submerged arc welding(SAW)process was used to rebuild this rail by utilizing a 1/8-in Lincore 40-S depositing wire.This study used four destructive tests:1)XRD residual stress measurement,2)SEM/OM analysis,3)hardness test,and 4)tensile test.The results showed that the required mechanical strength could be achieved.However,the repaired area seems more vulnerable to the forces encountered on a railroad network due to the more brittle structure due to high temperatures in this region.Considering this flaw is critical because forces are primarily dynamic in railway networks,especially in heavy rails,which are higher due to the extensive use of freight trains.
